I don't really know what to do for a baby- teen reader since I'm not exactly a fan of taking care of children (i do it anyways because i have siblings) but i tried :)
Third POV
One day Russia found a baby on his front porch, cliche I know. As he picked up the baby he saw a letter in the basket, it was some of your files. Your birth certificate states your full name. "Well (Y/N), I guess you're stuck with me." he says with a confused smile as he takes you and the basket inside. He sits and contemplates on the couch on what to do with you and the only thing he can think about is calling, in his own words, "that capitalist scum."
He finally decides call him asking for help it pretty much ended in them arguing and America teasing the hell out of him for not knowing how to take care of a baby. Long story short it ended up with a "Fine I'll come over in a minute." From America
Soon enough America came over to Russia's house. "Hey communist, what the hell did you want again?" America asked in a bored tone. Russia sighed and rolls his eyes "well capitalist, I need help with this baby" he says annoyed at America's antics. Russia then explained how he had found you on his porch and needed help on being reminded on how to care for a baby.
America proceeds to give his lessons and even went shopping for a crib and baby items.
As the day passed, Russia was reminded more and more and has understood how to take care of a baby. But at the same time America grew attached to you so they somehow got into a conversation then an argument and then an agreement.
The agreement was that in order to fill in both parenting roles, they had decided that they will take turns every week and every time you need to be babysat one of them goes to take care of you.